1. Field of the Invention
The present invention relates to an object detecting apparatus that detects an object using an ultrasonic sensor.
2. Description of the Related Art
US 2003/0034883 A (corresponding to JP-A-2003-57340) discloses an object detecting apparatus including an ultrasonic sensor. The ultrasonic sensor transmits an ultrasonic wave having a burst waveform and receives a reflected wave reflected by an object. When a level of the received signal is greater than a threshold value, the object detecting apparatus calculates a distance to the object based on a time from when the ultrasonic wave is transmitted until when the reflected wave is received. When the distance to the object is within a warning distance, the object detecting apparatus outputs a warning.
When the object detecting apparatus detects a noise signal that generates in a surrounding environment as a reflected wave by error, the object detecting apparatus is difficult to detect an object with a high degree of accuracy.
Thus, an object detecting apparatus having a noise resistance is proposed. Before the object detecting apparatus executes an object detection, the object detecting apparatus detects a noise signal received by a sensor and the object detecting apparatus determines existence or nonexistence of the noise signal by comparing a level of the noise signal with a threshold value. When the object detecting apparatus determines that there is no noise signal, the object detecting apparatus validates a detected result of the object detection. When the object detecting apparatus determines that there is a noise signal, the object detecting apparatus invalidates a detected result of the object detection.
In the above-described object apparatus, in order to detect an object at a long distance, it is required to reduce a level of the threshold value for detecting existence or nonexistence of the noise signal because a level of a reflected wave reflected by the object at the long distance is low. However, when the object detecting apparatus determines existence or nonexistence of the noise signal by using a lower threshold value, the object detecting apparatus may determine that there is a noise signal with higher frequency, and thereby an object detection accuracy may be reduced. That is, when the detecting distance is increased, the object detection accuracy may be reduced.